1. Field of the Invention
The invention relates to a device for moving and positioning an object in space, having at least three actuating arms that are each connected to a motor/transmission unit and are pivotable around a transmission axis, a support element provided for arranging at least one gripping mechanism for gripping the object; at its free end, each actuating arm has a first articulation axis extending parallel to the transmission axis, with first joint parts spaced apart from each other, each belonging to a respective first ball joint; the support element has a second articulation axis associated with each actuating arm, with first joint parts spaced apart from each other, each belonging to a respective second ball joint; the first articulation axis is connected to the second articulation axis by means of a pair of connecting rods that have second joint parts at the ends and, together with the first joint parts on the first articulation axis and the first joint parts on the second articulation axis, these second joint parts at the ends of the connecting rods form the first and second ball joints; and the connecting rods are connected to each other in order to stabilize the ball joints. The device for moving and positioning an object in space is a device referred to in professional circles as a robot with parallel kinematics.
2. Description of the Prior Art
A device with three parallelogram rod assemblies of the type mentioned at the beginning, which is also referred to as a “delta robot,” is known from WO-A-03/106114. The two connecting rods composed of a stiff material and belonging to a parallelogram have pairs of pins that protrude laterally in the region of the ball joints. Pairs of O-rings composed of a rubber-elastic material are elastically stretched into place around the pins on opposite sides of the connecting rods. The prestressing force produced between the two connecting rods holds the sockets against the balls. The prestressing also provides the required restoring moment that prevents the rods from twisting due to friction, dynamic forces, and forces exerted by components mounted on the rods such as vacuum hoses. In lieu of rubber-elastic O-rings, U.S. Pat. No. 6,419,211 has disclosed non-paired spring elements that have two angled elements with a compression spring situated between them.
In the event of an overload, i.e. when the loads on the joints become greater than the prestressing forces, the joints decouple, which is a desired safety function and prevents the destruction of the robot.
The elastomer elements currently used to produce a prestressing between the connecting rods are encumbered by the following disadvantages:                Material-related aging and fatigue phenomena: creeping, flowing, relaxation.        Application-related aging and fatigue phenomena due to: cleaning agents, UV, stresses extending into the plastic strength range, low environmental temperatures (brittleness).        Limited dimensional accuracy of the prestressing due to material tolerances.        Primary function not dimensioned for the absorption of required restoring moments for lateral hose routing on the connecting rods.        With gradual destruction of the prestressing element, it is not possible to assure detectability of falling components in products to be processed.        Limited possibility of predicting the service life due to the above-mentioned conditions.        Hygiene requirements make it impossible to use conventional spring elements such as steel springs.        
U.S. Pat. No. 6,516,681 has disclosed a robot with parallel kinematics that has four parallelogram rod assemblies.